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The Fender Bassman is a bass amplifier introduced by Fender during 1952. Initially intended to amplify bass guitars, the 5B6 Bassman was used by musicians for other instrument amplification, including the electric guitar, harmonica, and pedal steel guitars. Besides being a popular and important amplifier in its own right, the Bassman also became the foundation on which Marshall and other companies built their high-gain tube amplifiers.
The 5B6 Bassman
During 1952, the Fender 5B6 Bassman amplifier was introduced as a combo amplifier cabinet that included the amplifier chassis combined with one 15" speaker. The 1952–1954 5B6 Bassman amplifiers had two 6SC7 or 6SL7GT pre-amp tubes, two 5881 power tubes and a single 5U4G rectifier tube. It was designed to generate 26 watts at an 8 ohm impedance load, and offered a cathode-based bias.
From 1952 through the spring of 1954, Fender produced approximately 660 model 5B6 Bassman amplifiers (serial numbers #0001–0660). The earlier cabinets have been called "TV Front" designs, with a front panel that had a rectangular grill cloth with rounded corners and looked much like a television of that era. In 1953 the cabinet designs were changed to the so-called "Wide Panel" design, with a 5 inch wide tweed covered panel above and below a wider swath of grill cloth. Fender ceased production of 5B6 Bassman amplifiers during the spring of 1954.
The 5D6 Bassman with dual rectifiers
During November 1954, Fender introduced the newly designed 5D6 Bassman amplifier offering four ten inch speakers and was designed utilizing two rectifier tubes. The 5D6 was a major departure from the earlier 5B6 Fender Bassman model. Designed by Freddie Tavares, longtime R&D man at Fender, the new circuit included two rectifier tubes and became known as the Dual Rectifier Bassman. Instead of the single 15" speaker, four 10" Jensen Alnico P10R speakers were used. The circuit had two innovations: a fixed bias for the power tubes, which increased power in comparison to the earlier cathode bias design, and a cathodyne phase inverter, using half of the 12AX7 tube and allowing a third gain stage on the other half.
The first 4x10 Bassman amplifiers started with a batch of prototypes in November and December 1954, model 5D6. No schematic for the 5D6 circuit has ever been found, but Ken Fox and Frank Roy have created a few from originals, and copies are freely available online. Only 11 of these early 5D6 Bassman examples are known to have survived. The lowest serial number known to still exist is 0013 (Frank Roy), 0035 (Albert Talley), 0075 (Jim Cornett), 0077 (Perry Tate), 0089 (Mark Grandfield), 0701, 0745 (Walter Horton), 0769 (Hayes Kolb), 0780 (sold on eBay Nov 2006), 0783, and 0785 (Hayes Kolb) are among those still known to exist.
Narrow panel models, 1954 to 1960
Fender began making other models with tweed covering, a similar open backed cabinet with a rectangular grill cloth and a narrow (just over an inch wide) tweed covered panel at the top and bottom. Produced from 1954 until 1960, these models are called the "narrow panel" tweed amps .
Fender introduced the model 5D6 "DK" in November 1954 followed by the 5E6 Bassman Amp during early 1955. The 5E6-A Bassman model was introduced later that year and included some evolutionary improvements. Demand for the tweed Bassman amp grew, so Fender increased production. By the middle of 1957 more than 1,500 examples of the 5E6 series had been sold.
In July 1957, Fender introduced the model 5F6 Bassman. This model also had four Jensen P10R speakers, but the power supply was redesigned around a single 83 mercury vapor rectifier tube, and a new preamp circuit was introduced that included a three knob tone stack, with separate controls for Treble, Mid and Bass. The power amp included a "long tailed pair" phase inverter, an innovation that noticeably increased the "headroom" or clean power output capability of the amplifier. Similar preamp changes were also incorporated in the 5F8 Twin Amp at about the same time, but not on other large size Fender amps.
During 1958, Fender introduced the model 5F6-A Bassman model. This final 1950s Tweed Bassman model product line included a change from the 5Y3 to the GZ34 rectifier tube, as well as a modification within the Presence control circuit. During early 1960, Fender began producing the 5F6-A Bassman with Jensen P10Q speakers. The P10Q Jensen speakers are more able to manage stronger electrical input power and generate better "clean" output sounds than previous installed P10R Jensen speakers. The P10R Jensen speakers were shipped within all Fender Bassmen from late 1954 until early 1960. Many professional music industry analysts have heralded the 1950s Fender 4×10 Bassman amps as the greatest guitar amp ever. The first 1954 Fender Tweed 5D6 4×10 circuit generated further Tweed Bassman amplifier development through 1960. Several Bassman models were progressively influenced by the 5D6 through the last Fender Tweed 5F6-A Bassman's circuit design. The 5F6-A Bassman's design was directly copied by Marshall Amplifiers within their JTM-45 amplifier during the early 1960s.
In 1990, Fender began reissuing the 5F6-A Bassman. The first series of the reissue were made at the Corona, California facility, and came equipped with four Eminence-made 10" blue frame AlNiCo speakers, and a solid state rectifier unit. Later on, production was moved to Ensenada, Baja California, and the model name was altered to "59 Bassman LTD". The LTD came equipped with the original 5AR4 rectifier tube, and four Jensen P10R reissue alnico speakers, which was period correct for the original amp.
In late 1960, Fender introduced a completely redesigned model 6G6 Bassman Amp, using the "piggy-back" design, in which the amplifier chassis is housed in a small cabinet, attached by metal clips to a larger separate speaker enclosure.
The early models were called "Brownface" because of the dark brown color used on the control panel. The 6G6 model was covered in rough Blonde colored Tolex material with Oxblood colored grill cloth. It had a single GZ34 rectifier, two 5881/6L6GC power tubes and four 12AX7 preamp tubes. The output was 50 watts at 8 ohm into a single 12 inch speaker, with a "Tone Ring" baffle in the speaker cabinet. In early 1961, model 6G6-A was introduced with a solid state rectifier replacing the GZ34, and two 12 inch speakers with a conventional baffle in a slightly larger cabinet (wired in parallel) with a 4 ohm output. In 1962, model 6G6-B was introduced, which incorporated circuit changes but used the same speaker configuration. In 1963 smooth Blonde Tolex covering was used instead of the early rough texture cover, and a light tan grill cloth. In late, 1963, Fender changed the cosmetics to what is commonly known as the "blackface" scheme. This amp still had the presence knob and same circuit (designated 6G6-B) as the smooth Blonde Tolex Bassman, but the faceplace was now black, the Tolex was black, and the grillcloth had moved to a silver cloth with black thread. The logo had also transitioned from the flat cast tin Fender with the brown paint in the tail, to a plastic logo with faux chrome and more 3-D shape.
In 1964 Fender introduced the AA864 circuit, and changed the appearance to the "Blackface" design, with black tolex covering and a black painted control panel. Fender was sold to CBS in 1965, and the AA165 circuit was briefly introduced, before being replaced by the AB165 circuit. The "Blackface" design continued until the "Silverface" model was introduced in 1968. Early "Drip-Edge" Silverface Bassmen used the same AB165 circuitry as the previous Blackface versions. The Brownface, Blackface, and Silverface "piggyback head" (except the Bassman 10 and 20, which were also combo amplifiers) versions of the 1960s, 1970s, and early 1980s generally followed a trend toward cleaner sound and more headroom.
- Super Bassman (1969–1971) – one speaker cabinet
- Super Bassman II (1969–1972) – two speaker cabinets
- Bassman 10 (1972–1982) – Silverface combo – four 10" speakers, 50 Watts/RMS (models produced after 1977 came with a three-band EQ on the Bass channel and 75 Watts/RMS with ultra-linear output section).
- Bassman 50 (1972–1977) – Silverface piggyback head – two 15" speakers, 50 Watts/RMS – Same specs as the original silverface Bassman heads produced between 1968 and 1972, except for the addition of a tailless amp decal and an AC568 circuit.
- Bassman 100 (1972–1977) – Silverface piggyback head – four 12" speakers, 100 Watts/RMS.
- Bassman 135 (1978–1983) – Silverface piggyback head – Same as the Bassman 100, with 135 Watts/RMS, ultra-linear output section and a three band EQ on the Bass channel.
- Bassman 70 (1977–1983) – Silverface piggyback head – Same as the Bassman 50, with 70 Watts/RMS, ultra-linear output section and a master volume control.
- Bassman 20 (1982–1983) – Blackface combo – one 15" speaker
- '59 Bassman and '59 Bassman LTD (1990–present) – 5F6-A reissue
- "Fender Wide Panel Tweed Bassman". Ampwares.
- Wheeler 2007, p. 164.
- Ware, Mark. "Fender Amp Field Guide".
- Gagliano, Greg (April 2010). "Dating Fender Amps by Serial Number, Part VI". Vintage Guitar Magazine: 38–39, 100–101.
- Kuehnel, Richard (2009). Circuit Analysis of a Legendary Tube Amplifier The Fender Bassman 5F6-A. Pentode Press. pp. 12–15. ISBN 0976982250.